1. Field of the Invention
The invention relates in general to a signal processing apparatus and associated method, and more particularly to a signal processing apparatus capable of directly performing a signal conversion operation on a reception signal and associated method.
2. Description of the Related Art
Radio frequency identification (RFID) is a wireless communication technique, which, without establishing mechanical or optical contact between an identification system and a predetermined target, identifies the predetermined target and reads/writes associated data through radio signals. An RFID signal is an amplitude shift keying (ASK) modulation signal. In general, an envelope detector may be utilized for demodulating an RFID signal to remove carrier waves on the RFID signal while leaving envelopes containing data. Further, in order to reinforce demodulation sensitivity, the envelope detector includes an amplifier and an analog-to-digital converter (ADC) for converting data of the RFID signal to digital data and to feed the digital data to a digital signal processor (DSP). In another conventional approach, the RFID signal is down-converted by use of a mixer to generate a baseband signal, which is then converted to digital data further fed to a DSP. However, the above architecture suffers from the setback of complicated circuitry. Moreover, since the RFID signal can only be demodulated into effective data with significance after undergoing processes of several circuits, issues including distortion, a lowered signal-to-noise ratio (SNR) and an increased bit error rate are incurred as the RFID signal is affected by circuit linearity and bandwidth. Further, when a multi-stage amplifier is employed for amplifying the RFID signal, in order to prevent non-signal DC components from being excessively amplified, an AC coupling circuit is usually added in between for removing the DC components. However, if a high-pass corner of the multi-stage amplifier gets too high, low-frequency components in the RFID signal may also be filtered out to similarly lead to signal distortion. Conversely, to render a low high-pass corner, the size of a corresponding resistor or capacitor needs to be enlarged such that manufacturing costs of a chip are increased. Therefore, there is a need for a solution in the art for high-accuracy and low-cost RFID signal processing circuitry.